The present invention is generally related to medical devices, systems, and methods. In particular, the present invention is in the field of quality assurance and verification for radiosurgery or radiation therapy planning.
Radiosurgery and radiotherapy are hampered by motion of the patient during dose delivery. This motion results in less dose delivered to the target structure and, potentially, more dose delivered to critical structures than desired. Patients can be immobilized to reduce inadvertent motion but breathing, cardiac motion, and bowel motions are involuntary and cannot be prevented during the treatment period. A radiosurgery system has been developed (Accuray CyberKnife with Synchrony) that can detect breathing motion of the patient and move the radiation source to compensate for this motion. This system does not compensate for cardiac or other involuntary movements. Treatment plans can be created that take into account the reduction in precision produced by patient motion in order to predict the dose delivered to moving targets or critical structures.
Test objects have been developed that simulate movements due to respiration. Wong et al. [K H Wong, S Dieterich, J Tang, K Cleary, Quantitative Measurement of CyberKnife Robotic Arm Steering, Technology in Cancer Research and Treatment, 6:589-594, (2007)] describe using motion tables to simulate respiratory motion of a lung tumor and skin motion simultaneously for testing of the Accuray CyberKnife system. The Wong system allows a radiation detector to be moved in three dimensions to accurately reflect the position of a lung tumor while light emitting diodes are moved to reflect the position of the skin on the chest.
Accuray and Computerized Imaging Reference Systems, Inc (CIRS) jointly developed a simpler test object for testing Accuray's CyberKnife with Synchrony system. This test object consists of two motors. One motor provides inferior-superior motion of a radiation detector and vertical motion of LED's (chest motion). A second motor rotates the radiation detector in an arc to provide additional motion.
Both the Wong and the Accuray/CIRS test objects are designed to use a fiducial in the radiation detector that can be used for alignment with the radiation delivery system. This fiducial is automatically detected by an x-ray imaging subsystem. The radiation source is then moved based on the position of the fiducial.
Neither the Wong or the Accuray/CIRS test objects has been applied to the motion of the heart. The contractile motion of the heart is substantially faster than the respiratory motion that these test objects were designed to mimic. It is speculated that the contractile motion of the heart is too fast for the Accuray CyberKnife Synchrony system to track. The Wong and CIRS/Accuray test objects are used to test the motion that is tracked and not to test the compensation applied in the treatment planning stage for motion that is not compensated.
The heart exhibits complicated motion due to contraction. This motion causes different parts of the heart to move in significantly different ways. Therefore, tracking fiducials that are not located on the target area can subject the treatment to some error. This may, however be acceptable if the treatment area is not conducive to the placement of fiducial markers. The differential motion between the fiducial location and the treated location can be compensated in the treatment plan. However, the test objects developed by Wong and CIRS/Accuray do not have any provision for differential motion between the fiducial and the radiation detector.
In light of the above, it would be desirable to develop a target motion simulator system having both respiratory and cardiac motion for use in verifying target tracking with a radiosurgery or radiation therapy device. It would be particularly beneficial if the systems were compatible with existing radiosurgery or radiation therapy systems.